Method and composition for rendering window surfaces water repellent and product resulting therefrom



Patented Sept. 30, 1952 UNITED STATES PATENT OFFICE- METHOD AND COMPOSITION FOR RENDER- ING WINDOW SURFACES WATER ,REPEL- LENT AND PRODUCT RESULTING THERE- FROM Donald F. Stedman, Ottawa, Ontario, Canada, assignorto The Honorary Advisory Council for Scientific and Industrial Research, Ottawa, 011-. tario, Canada, a corporation of the Dominion of Canada No Drawing Application June 18, 1947, Serial No. 755,490. In Canada March 7, 1945 This invention relates to methods and compositions for the treatment of glass and plastic windows, in a manner such that they will not wet with water." It is particularly concerned with the problemof rendering aircraft windows rain repellent so that clearvision may be maintained,-

but' it isalso applicable to the maintenance of clear vision throughwindscreens, lenses orother optical surfaces, subjected to rain or water spray" in various locations, such as periscopes, binocula'rs,-boats,- motor cars, locomotives and the like.

It is to be noted that-there is a critical dis-. tinction' between" an anti-misting treatment which causes water on a, lens orwindow to spread in a thin uniform film and the treatment of the present-inventionwhich causes water to collect inspherical droplets which grow until they roll down or are blown away by the wind when. the

cally unchanged. Thus where'accuracy of vision is necessary it produces a much better result, and if wind is also present the difference is enhanced, since'the result produced by the antifog becomes worse, but the effect of the repellent is better. a v Recording the appearance of relatively distant This is'due to the fact that the,

13 Claims. (Cl. 1-1792) objects through windscreens subjected to rain is a problem in optics'of considerable complexity.

The presentinvention is the result of an internsive investigation of all the factors involved.

:1 The object of the present invention is to provide a treatmentfor Windshields and the like" which'insures: ease of application without too I greatly skilled personnel; clarity of vision with reference to the optical quality of the coatingfilm as well as the perfection with which it repels the water; long life per application including lack of damage by light, the heat of the sun, weather exposure or flight under dry conditions;

ease of renewal of the repellent coating; freedom from damage byde-icing procedures, spattering' with oil and the like; that the coating should not that it should clean collect dirt too rapidly and readily.

A more specific object of the invention is to provide a new composition which is itself rain repellent and which provides a particularly good attachment between a wax coating and the glass, and a method of activating such composition.

/ Other objects and advantages of the invention will appear from the following description.

Of all classes. of substances, the water repellent non-p'olar waxes come nearest to fulfilling these requirements, but it is well known that such non-polar substances'will not adhere to a highly polar substance such as glass, andflthemainobject of this invention is to provide'a method by which the glass is causedto. become 7 Its nature is then similar to the above mentioned waxes and a non-polar water repellent surface.

these waxes therefore adhere well.

This application is a continuation-in-part of application Serial No. 582,426 filed May 12, 1945,

now abandoned."

It has been found that an excellent non-polar Water repellent surface can be secured on glass by the use of strong friction while rubbingit with an alkyl. or aryl subs'tituted poly silicarie, of

is a type compound. [All compounds of this'class.

in which the silicon chain consists of two' or more'sili'con atoms are combined with hydrocarbon groups, are active in this respect. Theymay" be varied in the following manners and still pro-f du'cel excellent results:

(a) Although the" similarly substitutedmono silicanes, which may be considered as derived I from SiI-Ii by substituting hydrocarbon groups for H, are active to some extent, .theyare much inferior to the hydrocarbon substituted poly-f silicanes in which av chain of "silicon atomsis present. If conversely the silicon chain is ange than two atoms the resultsare slightly better;

ib) The hydrocarbon groups may be varied alf I. most indefinitely, any alkyl or aryl hydrocarbon' g roup, e. g., methyl, butyLlauryl, cetyl, phenyl and generally'any member of the hydrocarbon groups may beused; V

(c) The substituted hydocarbon. groups need not be the same. If all'the substituent hydrocarbons are methyl the best results are not obtained If, onrthe vother hand, all have, for example-l6 carbon atomstheresulting film on the window surface'becomes visible. 1 a

(dlUnsaturated hydrocarbon groups may be; substituted for some of the saturated hydrocar+ The following. are illustrativeof these poly-silicanes. The particular position of;

bon groups.

For this purpose'any wax of this class is helpful, but in order to secure optimum results a rather closely adjusted composition has been found best. Preferably the wax composition used should be as free as possible from polar constituents. -The preferred composition is a combination of a tough, hard non-polar mineral wax, a.

relatively soft non-polar paraffin wax substantially free from oil and of great water repellence,

polyethylene and a non-polar fiberizing compo' nent such as polyisobutylene. Butyl rubber may be used but its slight unsaturation produces some instability to ultra violet light. For this reason polyisobutylene is preferred. The polyethylene facilitates polishing, gives more water repellency over a longer period of time and permits use of harder wax. 3 to of it may be used. 6.4% is preferred.

The mineral wax component if not already adequately non-polar may be treated with sodium metal atsubstantially 250 C. followed by treatment with activated bentonite and filtra' tion. For example 400 grams of an amorphous mineral wax having a melting point of substantially 93 C. was heated with 20 grams of sodium metal to 250 C. for 1% hours. The wax was decanted from the sodium, cooled to its melting point, treated with 25 grams activated bentonite, heated to 175 C. for 10 minutes, again cooled to its melting point and treated with a further v Per cent Purified amorphous mineral wax. 19-38 Paraffin wax (M. P. 64 C. or higher 49-70 Polyisobutylene 3-10 Polyethylene 3-10 The following is illustrative of the composition of the preferred wax coating material, which. may be provided in the form of a stick, as apaste or as a liquid thinned out with enough solvent to spray on the surface.

An example of the wax mixture made as a paste is as follows: 1

Per cent by weight Purified mineral wax 29.0 Parafin 57.9 Polyisobutylene 6.7 Polyethylen mixture as a thin liquid for use in reviving coatgrams of bentonite, and filtered hot. About 360 grams of pale yellow wax was obtained. It is extremely tough and moderately hard and has a high receding angle for water droplets The composite wax mixture should contain between substantially 19% and 38% of such purified amorphous mineral wax. portion is 29.07%.

For the parafiln component a high grade commercial paraffin wax having a melting point'of 64 C. or higher is used, and needs no further purification. I-Iarder paraffin waxes are rather crystalline and therefore permit polishing over a wider range of temperature, while the softer waxes cause difficulty in polishing the film, as they streak easily. When judged by the criterion of high receding angle forwater droplets, paraffin wax is the mostrepellent of the waxes, but too high proportions prevent proper polishing.

Accordingly the composite mixture should contain not more than substantially 70% nor less than 49% of paraflln wax, while the preferred proportion is substantially 57.9%.

.The standard grade of polyisobutylene' of.

about the consistency of raw rubber and having a Shore hardness of about 20-30 is purified by dissolving as 2% solution in petroleum ether of spots of a rubber-like nature develop while at tempting to polish the wax. This efiect therefore limits the useful addition of this ingredient. The composite material preferably contains 6.7% of the reprecipitated polyisobutylene. The proportion should not be less than 3 nor more than The composition of the nonpolar coating as follows The preferred pro: v

has a viscosity in poises at 130 C. from 3 to ings during flight. In this case it is best to use an excess of the mineral wax, since it crystallises out on cooling the solution and must :be filtered off and discarded:

Per cent by weight Purified amorphous mineral wax 47.6 Paraflin wax 47.6 Reprecipitated polyisobutylene 2.4 Polyethylene 2.4

100 grams of this mixture is dissolved in e. g. xylol- 19,000 cc. with heat, cooled to 20 C. and filtered. To the filtrate, which now contains the solid components within the range of compositions stated above to be desirable, are added 19,000 cc. of petroleum solvent (naphtha as above). Although these wax proportions are pre ferred, owing to the somewhat variable nature of Waxes, as natural products, it is necessary'to adjust the proportions to suit every batch of wax 1n order to maintain the proper hardness at both low and high temperatures.

Shore Durometer Type A hardness of the polylsobutylene used was20 to 30. Polyethylene used Since the amount of wax applied to the glass is very small, of the order of 30 mg. per ten sq.

vent water running off as easily'and reduce the useful life of the coating. Accordinglythe cloth is subjected to a very thorough washing, rinsing and drying, followed by extraction with methanol and benzene in an apparatus which boils the solvent and returns the pure distillate. over the cloth continuously. For best results the cloth is so extracted with about times its weight of methanol and benzene. If ethanol and benzene areused about 250 times the weight of the cloth should be used. Such a treatment removes from the cloth as much as 0.75% of its weight'of wax of a non-repellent type and leaves a fabric having less than one milligram of polar compounds per ten'square decimeters of cloth area. The cloth is then considered to be free from these polar compounds.

Rayon'cloth made from high quality wood pulp or cotton linters may be used. It is important that no sizing be present in the finished cloth. Papers made from rayon fibers may also be used providedv they contain no deleterious substances.

.The rain repellent treatment is appliedas follows: The surface to be coated is thoroughly cleaned with a cloth free from polar compounds by rubbing with cellite (a fine diatomaceous earth) and water. The poly-silicane composition or paste containing carbon black and solvent is then applied with the cloth, usingsufi'icient friction to activate the silicane. The carbon black is wiped off, leaving a clean surface. For aircraft windows the composite wax preparation is then applied with the cloth. When it dries it is polished with a dry cloth. The glass is then highly repellent to water and the film coating is so strong that flight through rain does not damage the surface. It is also not damaged by de-icing procedures; 7 This treatment can be applied at any temperature from 40 F. to +135 F. The only variations in technique needed are the use of methyl or ethyl alcohol, denatured or otherwise, instead of water for cleaning the glass below the freezing point, anda second wet polishing at high tem-- peratures when the usual dry polishing leaves a slightly smeared surface.

Throughout this specification glass is understood either as the usual glass, or as transparent plastic material serving the same purpose.

As compared with previously known procedures the present treatment has many advantages. It can be applied quickly anywhere; it has long life; it gives very clear vision in rain without using wipers; the film is invisible and free from optical distortion; the materials used are stable in storage, are non-corrosive and free from harmful constituents; it is helpful in preventing scratching of plastics; it can be readily renewed; it is relatively inexpensive; it is not damaged by oil, gasoline, alcohol or glycol.

It is to be understood. that variations may be made Without departing from the spirit or scope of the invention as "defined in the appended claims. By non-polar wax, as used herein, is meant a compound consisting only of carbon and hydrogen atoms (hydrocarbon), which has-been purified to remove substantially all polar compounds.

I claim:

1..A method of rendering window surfaces water and rain repellent which comprises applying thereto a substituted polysilicane, consisting only of .carbon, hydrogen and silicon and having not less than one Si-Si linkage and at least one of a group consisting of alkyl and aryl radicals attached to at least one Si atom in said linkage, in admixture with a volatile hydrocarbon solvent and a finely divided inorganic, non-siliceous adhesion-promoting agent which with rubbing changes said poly-silicane from a form which is soluble in hydrocarbon solvent to one which is insoluble. therein and selected from the group consisting, of carbon black, rouge, barium sulphate, lithopone and the precipitated fluorides of calcium, barium, strontium and lithium, and rubbing the mixture on the surface to cause the polysilicane to adhere to itin the form of a film which is i nert to oil, gasoline, alcohol and glycol.

2. A method as defined in claim 1 wherein there is applied to said film a water repellent ax which is essentially non-polar.

3. A method as'defined in claim 1 wherein there is applied to said film coating a non-polar composition consisting essentially of 19 to 38% by Weight of purified amorphous mineral Wax having a melting point of substantially 93 C., 49 to by weight of a parafiin wax having a melting point of at least 64 C., 3 to 10% of polyisobutylfaces water and rain repellent comprising essen-- tiallysubstituted polysilicane, consisting only'of carbon, hydrogen and silicon and having not less than one Si-Silinkage-and at least one of a group consisting'of alkyland aryl'radicals attached to at: least one Si atom in said linkage," in admixture-in a volatile hydrocarbon solvent with a finely divided, inorganic,- non-siliceous adhesivepromoting agent which with rubbing changes said poly-silicane from a form which is solublein hydrocarbon solvent to one which is insoluble therein and selected from a group consisting of carbon black, rouge, barium sulphate, lithipone andthe precipitated fluorides of calcium, barium, strontium and lithium.

-6. A- composition for rendering window surfaces water and rain repellent comprising essentially substituted polysilicane, consisting only of carbon, hydrogen and silicon and having not less than one Si-Si linkage and at least one of a group consisting of alkyl and aryl radicals attached to atleast one Si atom in said linkage, in admixturev with a volatile hydrocarbon solvent and acetylene.

black.

'7. A composition for forming with rubbing a rain repellent essentially non-polar film on window surfaces, consisting of hexa-ethyl disilicane and carbon black in a volatile hydrocarbon solvent.

8. A composition for forming with rubbing a Water repellentessentially non-polar film on window surfaces, consisting of hexabutyl disilicane and carbon black in a volatile hydrocarbon sol' produced by the method defined in claim 1 and consisting essentially of adherent substituted polysilicane consisting only of carbon, hydrogen and silicon and having not less than one Si-Si linkage and at least one of a group consisting of alkyl and aryl radicals attached to at least one Si atom in said linkage.

11-. A window surface having thereon a composite film consisting essentially of adherent substituted polysilicane consisting only of carbon,

hydrogen and silicon and having not less than one Si-Si linkage and at least one of a group consisting of alkyl and aryl radicals attached to at least one Si atom in said linkage, and on the adhering polysilioane a non-polar wax composition consisting essentially of 19 to 38% by weight of purified amorphous mineral wax having a melting point of substantially 93 C., 49 to 70% by weight of a parafiin wax having a melting point of at least 64 C., 3 to 10% of polyisobutylene and 3 to 10% of polyethylene.

12. A window surface as defined in claim 11 wherein the polyisobutylene has a Shore Durometer Type A hardness of 20 to 30.

13. A window surface produced by the method defined in claim 2 having thereon a film consisting essentially of adherent substituted polysilicane consisting only of carbon, hydrogen and silicon and having notless than one Si-Si linkage and a non-polar water repellent wax on said film.

DONALD F. STEDMAN.

- 10 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

5. A COMPOSITION FOR RENDERING WINDOW SURFACES WATER AND RAIN REPELLENT COMPRISING ESSENTIALLY SUBSTITUTED POLYSILICANE, CONSISTING ONLY OF CARBON, HYDROGEN AND SILICON AND HAVING NOT LESS THAN ONE SI-SI LINKAGE AND AT LEAST ONE OF A GROUP CONSISTING OF ALKYL AND ARYL RADICALS ATTACHED TO AT LEAST ONE SI ATOM IN SAID LINKAGE IN ADMIXTURE IN A VOLATILE HYDROCARBON SOLVENT WITH A FINELY DIVIDED, INORGANIC, NON-SILICEOUS ADHESIVEPROMOTING AGENT WHICH WITH RUBBING CHANGES SAID POLY-SILICANE FROM A FORM WHICH IS SOLUBLE IN HYDROCARBON SOLVENT TO ONE WHICH IS INSOLUBLE THEREIN AND SELECTED FROM A GROUP CONSISTING OF CARBON BLACK, ROUGE, BARIUM SULPHATE, LITHIPONE AND THE PRECIPITATED FLUORIDES OF CALCIUM, BARIUM, STRONTIUM AND LITHIUM.
 11. A WINDOW SURFACE HAVING THEREON A COMPOSITE FILM CONSISTING ESSENTIALLY OF ADHERENT SUBSTITUTED POLYSILICANE CONSISTING ONLY OF CARBON, HYDROGEN AND SILICON AND HAVING NOT LESS THAN ONE SI-SI LINKAGE AND AT LEAST ONE OF A GROUP CONSISTING OF ALKYL AND ARYL RADICALS ATTACHED TO AT LEAST ONE SI ATOM IN SAID LINKAGE, AND ON THE ADHERING POLYSILICANE A NON-POLAR WAX COMPOSITION CONSISTING ESSENTIALLY OF 19 TO 38% BY WEIGHT OF PURIFIED AMORPHOUS MINERAL WAX HAVING A MELTING POINT OF SUBSTANTIALLY 93* C., 49 TO 70% BY WEIGHT OF A PARAFFIN WAX HAVING A MELTING POINT OF AT LEAST 64* C., 3 TO 10% OF POLYISOBUTYLENE AND 3 TO 10% OF POLYETHYLENE. 